Biomacromolecules are constituents or products of living cells and include proteins, carbohydrates, lipids, and nucleic acids. Detection and quantification as well as isolation and purification of these materials have long been objectives of investigators. Detection and quantification are important diagnostically, for example, as indicators of various physiological conditions such as diseases. Isolation and purification of biomacromolecules are important for therapeutic purposes such as when administered to patients having a deficiency in the particular biomacromolecule, when utilized as a biocompatible carrier of some medicament, and in biomedical research. Biomacromolecules such as enzymes which are a special class of proteins capable of catalyzing chemical reactions are also useful industrially; enzymes have been isolated, purified, and then utilized for the production of sweeteners, antibiotics, and a variety of organic compounds such as ethanol, acetic acid, lysine, aspartic acid, and biologically useful products such as antibodies and steroids.
In their native state in vivo, structures and corresponding biological activities of these biomacromolecules are maintained generally within fairly narrow ranges of pH and ionic strength. Consequently, any separation and purification operation must take such factors into account in order for the resultant, processed biomacromolecule to have potency.
Chromatography is a separation and purification operation that is often performed on biological product mixtures. It is a technique based on the interchange of a solute between a moving phase, which can be a gas or liquid, and a stationary phase. Separation of various solutes of the solution mixture is accomplished because of varying binding interactions of each solute with the stationary phase; stronger binding interactions generally result in longer retention times when subjected to the de-binding effects of a mobile phase compared to solutes which interact less strongly and, in this fashion, separation and purification can be effected.
Efforts to utilize polydisperse particles as stationary phases for separating biomacromolecules by incorporation within a porous fiber matrix are disclosed in U.S. Pat. Nos. 4,384,957 and 4,488,969. Resultant composite sheet structures were cut into circular shapes and stacked to form columns.
Liquid cartridge filters have been developed over the years which represent a highly efficient format for the interaction of a liquid stream and a solid matrix. Furthermore, these filters operate at relatively high flow rates, e.g., liters per minute, and at relatively low pressures.
In tangential flow or radial membrane cartridge filters, the filtering element is presented in a plane parallel to the liquid stream flow, and two effluents or permeates are produced, one filtered or processed by passing through the filtering element and another not. While these filter arrangements operate at low pressures and the unprocessed permeate can in theory be recycled, these systems are intrinsically more complicated and slower to completely process a liquid stream because of relatively low flow through the element; also, if filtering elements were modified in some fashion to retain biomacromolecules, complete retention would be required in one pass through the element.
In "dead end" filters the filtering element is presented perpendicularly to the direction of flow of the liquid stream. All the liquid stream is required to pass through the element and only one permeate is produced. Considered as a separation unit in which separation is occurring by interaction with a stationary phase on or within the filtering element, the dead end cartridge filter would be analogous to a very wide, but shallow column. At high flow rates single pass retention of the biomacromolecule may be relatively low but by repeatedly cycling the effluent high percentages of the biomacromolecule can be retained.
Bioseparations have been conducted using modified filter cartridges. U.S. Patent No. 5,155,144 discloses microporous sheets comprising modified polysaccharide particulates such as diethylaminoethyl cellulose, a typical ion exchange chromatography stationary phase, dispersed within a polymeric medium. It is suggested that these sheets can further be configured into a dead end filter cartridge. Employing recirculation of effluent, a lead ion treated resin was evaluated as a generally shallow column between two stainless steel grids for the analytical separation of D-xylose (cf. A. M. Wilhelm and J. P. Riba, J. Chromatog., 1989, 484, 211-223). The resulting packed bed reactor system was evaluated to determine hydrodynamic conditions for particles for ultimate employment in columns for production liquid chromatography at relatively high system pressures and low flow rates.
U.S. Pat. No. 4,774,004 discloses the use of cartridge filters that are generally "charged" with filtration aids which are layered silicates that essentially function as ion exchange media and, optionally, kieselguhr or activated carbon. The resultant structures were useful for removing surfactants and "dissolved soil" from dry cleaning solvents. Details of the charging procedure, quantities of filtration aids employed, recycle flow rates, and operating system pressures are scant. No separation of one or more biomacromolecules was conducted nor contemplated.